There have been commercially available digital cameras each of which uses a memory card having a solid-state memory element as a recording medium, and records and plays back still and moving images sensed by a solid-state image sensing element such as a CCD. Such digital camera generally performs photographing processing of temporarily storing output data from an image sensing element in a buffer memory, and developing/compression processing of executing image processing and compression processing for the stored data and storing the data in the buffer memory again. The resultant data are written in a removable recording medium.
Various algorithms have been proposed for white balance (WB) control for a recording image, and WB control is executed as follows. After photographing, raw data which is output from an image sensing element, stored in a memory, and not subjected to signal processing is read out. A coefficient for each color that is determined by the color filter of the image sensing element is decided by a predetermined algorithm (this processing will be referred to as WB calculation hereinafter). A WB coefficient obtained as a result of calculation is multiplied to correct white data. After that, developing/compression processing is done.
Image sensing elements are classified into a progressive scanning type of line-sequentially reading out data from all pixels, and an interlaced read type of reading out data every other line in two fields.
In a conventional multi-field read method, WB calculation starts after raw data of one frame are written in a memory.
According to this method, read from the image sensing element and WB calculation can only sequentially operate. This does not generate a time lag until exposure starts after the shutter button is pressed, but takes a long time until an image confirmation display appears after photographing. In sequential shooting, the WB coefficient for the first image can be adopted. However, the first image undergoes WB calculation after raw data of one frame are stored in the buffer memory after photographing. The photographing interval between the first and second images becomes longer than the photographing interval between the second and subsequent images.
To solve this, the present applicant has proposed a method of reading out one frame in two fields and executing WB calculation during read of the second field, as disclosed in Japanese Patent Application No. 2001-273014 (US patent application Ser. No. 10/238,332, US filing date: Sep. 9, 2002). A multi-field read type image sensing element which reads out one frame in more than two fields, e.g., three or more fields can effectively utilize the light-receiving portion. While the sensor size is suppressed small, the number of pixels can be increased. It is therefore an object of the present invention to provide an improvement of the prior invention.